Interleukin 1β Up-Regulates mRNA Expression of Inducible Nitric Oxide Synthase in 3T3-L1 Preadipocytes: Role of JAKs/STATs, PKCs, and Src

Recent evidence suggests obesity as a low or systemic chronic inflammation. (Pre) adipocytes in the adipose tissue (AT) express and secrete a variety of cytokines and adipokines. Inducible nitric oxide synthase (iNOS) is an inflammatory enzyme involved in the production of NO. Until now, the inducer(s) of iNOS expression in (pre)adipocytes remains unclear. In this study, we investigated the effects of proinflammatory cytokines [interleukin-1β (IL-1β), IL-10, IL-12, interferon-γ (IFN-γ)], adipokines [retinol-binding protein 4 (RBP4), adiponectin, leptin, and resistin], and lipopolysaccharide (LPS), a bacterial cell wall component, on the expression of iNOS in 3T3-L1 preadipocytes. Notably, treatment with IL-1β at 20 ng/mL for 4 h markedly increased iNOS mRNA expression in 3T3-L1 preadipocytes, but that with IL10 (10 ng/mL), IL-12 (5 ng/mL), IFN-γ (10 ng/mL), RBP4 (5 ug/mL), adiponectin (100 ng/mL), leptin (100 ng/mL), and resistin (100 ng/mL), and LPS (1 ug/mL) for 4 h had little or no effect on it. Results of dose-response and time-course experiments confirmed the ability of IL-1β at 20 ng/mL for 4 h to maximally induce iNOS mRNA expression in 3T3-L1 preadipocytes. Importantly, pharmacological inhibition studies demonstrated that treatment with AG490 [an inhibitor of Janus-activated kinases (JAKs) and signal transducer and activator of transcription proteins (STATs)], GO6976 (an inhibitor of PKCs), or PP1 (an Src kinase inhibitor) suppressed IL-1βinduced iNOS mRNA expression in 3T3-L1 preadipocytes, pointing out the involvement of JAKs/STATs, PKCs, and Src in the process. This work advocates that IL-1β is a major and strong inducer of iNOS expression in 3T3-L1 preadipocytes.